| Traditional dredging methods often have problems such as low dredging accuracy,serious silt escape and siltation,high maintenance cost,and limited use.The air-lift dredging system has the characteristics of simple structure,low maintenance cost,no mechanical moving parts,no need to consider lubrication and wear problems,high work safety and reliability,and is suitable for river and lake reservoir dredging projects with high environmental protection requirements and large dredging depth.In order to further explore the internal flow mechanism and hydraulic characteristics of the air-lift system,an experimental bench of the air-lift dredging system is built in this paper.The diameter of the lifting pipe is 30 mm and the length of the pipe is 2320 mm.The gas-liquid two-phase flow and gas-liquid-solid three-phase flow experiments are carried out for the system.Based on Fluent software,the three-dimensional numerical simulation of gas-liquid two-phase flow in the system is carried out.The main research results of this paper are as follows:(1)In the gas-liquid two-phase flow experiment,the liquid lift flow rate increases with the increase of submergence rate(0.3,0.4,0.5,0.6,0.7,0.8)under the same air intake.Under the same submergence rate,the liquid lifting flow rate increases first and then decreases with the increase of air intake,and reaches the peak when the air intake is near 16m~3/h;the lifting efficiency of the system increases first and then decreases with the increase of air intake,and with the increase of submergence rate,the peak efficiency of the lifting system increases,and the maximum efficiency value of the system corresponds to the decrease of air flow.Under the specific conditions of submergence rate of 0.5 and air intake of 2m~3/h,when the liquid lifting flow is stable,it fluctuates around 0.125kg/s.The inlet pressure and the pressure difference between the inlet and the riser outlet fluctuate around 8.2kPa and 7.0kPa respectively.The high-speed camera is used to capture the gas-liquid two-phase flow pattern in the middle of the riser,which is dominated by slug flow and churn flow.(2)In the gas-liquid-solid three-phase flow experiment,the liquid and solid lifting flow increases with the increase of submergence rate(0.3,0.4,0.5,0.6,0.7,0.8)under the same air intake.Under the same submergence rate,the liquid and solid lifting flow rate increased first and then decreased with the increase of air intake,and reached the peak when the air intake is near 16m~3/h;the liquid lifting efficiency decreases with the increase of air intake.When the submergence rate is 0.3 to 0.6,the solid lifting efficiency increases first and then decreases with the increase of air intake.When the submergence rate is 0.7 and 0.8,the solid lifting efficiency decreases with the increase of air intake.The total efficiency of the system increases first and then decreases with the increase of air intake.Under the same working conditions,the liquid lifting flow rate in the gas-liquid-solid three-phase flow experiment is smaller than that in the gas-liquid two-phase flow.Under the specific conditions of submergence rate of 0.5 and air intake of 2m~3/h,the liquid lifting flow fluctuates around 0.1kg/s after stabilizing.The gas-liquid-solid three-phase flow behavior in the middle of the riser is captured by a high-speed camera.Due to the addition of solid particles,the three-phase flow is more complex than the two-phase flow,and the particles show three-dimensional irregular upward motion.(3)Modeling and meshing of simplified 3D model of air-lift system using ICEM software.Based on Fluent software,SIMPLE algorithm,Eulerian multiphase flow model and Standard k-ωturbulence model are used to carry out three-dimensional numerical simulation of gas-liquid two-phase flow in the air-lift system.The calculated liquid lifting flow rate is compared with the liquid lifting flow collected by the experiment.The error is within 10%,and the numerical simulation results are in good agreement with the experimental results.The radial distribution of liquid velocity at the inlet of the riser is decreasing from the pipe wall to the pipe axis,and the radial distribution of liquid velocity in the middle and outlet of the riser is decreasing from the center of the pipe to the pipe wall.The liquid velocity gradient near the pipe wall changes greatly,while the velocity distribution in the center of the pipe is relatively flat.The research results of this paper provide theoretical guidance for the design optimization of air-lift system,and lay a foundation for the popularization and application of air-lift technology in the field of dredging. |
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